The present application is the national stage under 35 U.S.C. 371 of PCT/JP00/03565, filed Jan. 6, 2000.
The present invention relates to organic metal complexes, and more particularly, to novel formazan metal complexes which are useful as light-resistant improvers for light absorbents and organic dye compounds.
As a new development in the fields of information recordings and displays, the following organic dye compounds are being rapidly increased in their demand: For example, in the former field, organic dye compounds having laser action or sensitivity to laser beams; and in the latter field, organic dye compounds having electroluminescence ability as well as those having laser action. In these days called an information technology era which requires improvement of the performance of information recording and displaying means, magnification of recording-capacity, downsizing, and satisfactory storage-stability, it has been more increased in demand for organic dye compounds having superior optical properties than the past, and this results in a development of a diversified organic dye compounds one after another. Organic dye compounds, however, have relatively-low light resistance as a whole and change in themselves to lose their inherent properties when exposed with light or allowed to illuminate repeatedly. For example, polymethine dyes, which are frequently used in optical recording media such as CD-Rs (a write-once memory using compact disc) and digital versatile disc recordable (DVD-R, a write-once memory using digital video disc) that are all highlighted as high-density information recording media, are susceptibly oxidized and decomposed by singlet oxygen, generated when the polymethine chains are exposed with reading and environmental lights. Since optical recording media are required to have at least 10 years of shelf-life, and therefore, to attain the requirement in this field, the research for light-resistant improvers applied for organic dye compounds is most energetically carried out.
To solve the problem of polymethine dyes, there has been proposed a light-resistant improver comprising a formazan metal complex. The formazan metal complexes as proposed in Japanese Patent Kokai Nos. 295,079/96, 151,863/98, and 337,958/98 are effective in improving the light resistance of polymethine dyes, however, they have the following problems: Since they have relatively-low solubility in organic solvents, which are used frequently in preparing optical recording media, and have insufficient compatibility with dyes, the processibility and the product yield may be lowered due to the crystallization of the polymethine dyes and metal complexes when the light-resistant improvers are added in an amount up to a level of sufficiently improving the light resistance of the dyes in preparing optical recording media, while the desired properties and features of the final products could be hardly attained when the amount of light-resistant improvers is set to a relatively-low level.
In view of the foregoing, the object of the present invention is to provide formazan metal complexes, which have satisfactory solubility in organic solvents and compatibility with dyes, and which can be applicable to organic dye compounds and improve their light resistance without substantially deteriorating their preferable light properties. The term xe2x80x9corganic dye compoundsxe2x80x9d as referred to in the present invention means organic dye compounds in general having sensitivity to light, and significantly relates, for example, to polymethine dyes such as cyanine dyes.
The energetic study and screening of the present inventors found that, when applied to organic dye compounds including polymethine dyes, formazan metal complexes, which have as ligands formazan compounds having a pyridine ring at the C-5 of formazan skeleton and having either a pyridine ring, furan ring, or straight or branched alkyl group at the C-3 of formazan skeleton, or which have tautomers of the formazan compounds, can improve the light resistance without substantially deteriorating the desired light-properties of the organic dye compounds and effectively inhibit the undesirable changes such as deterioration, fading, discoloration, and denaturation due to the exposure of reading and environmental lights. They also found that the formazan metal complexes of the present invention neither crystallize in themselves nor reduce the solubility of organic dye compounds even when applied to the compounds at a relatively-high concentration because the formazan metal complexes have relatively-high solubility in organic solvents and satisfactory compatibility with organic dye compounds. The present invention was made based on the creation of the novel formazan metal complexes and the finding of their industrially-useful features.